Simulation Research on Coal-Water Slurry Gasification of Oil-Based Drill Cuttings Based on Fluent

In this paper,based on Fluent software,a five-nozzle gasifier reactor was established to simulate the gasification process of oil-based drill cuttings coal-water slurry.The influence of concentration and oxygen/carbon atomic ratio on the gasification process of oil-based drill cuttings coal-water slurry was investigated.The results show that when the oxygen flow is constant,the outlet temperature of gasifier decreases,the content of effective gas increases,and the carbon conversion rate decreases with the increase of concentration;When the ratio of oxygen to carbon atoms is constant,the effective gas content rises and the temperature rises with the increase of the concentration,and the carbon conversion rate reaches the maximum value when the concentration of oil-based drill cuttings coal-water slurry is 65%;When the concentration is constant,the effective gas content decreases and the outlet temperature rises with the increase of the oxygen/carbon atom ratio,and the carbon conversion rate reaches 99.80%when the oxygen/carbon atom ratio is 1.03.It shows that this method can effectively decompose the organic matter in oilbased drill cuttings and realize the efficient and cooperative treatment of oil-based drill cuttings.

Generalized equation for calculating rock cutting efficiency by pulsed water jets

One of the promising methods for rock cutting technology is the use of high-speed water jets.In order to improve the cutting capacity of water jets without increasing the hydraulic power of equipment,pulsed water jets are basically used to increase the rock cutting efficiency.However,there are no mature recommendations for selection of rational parameters,and the relationship between indicators of rock cutting efficiency and parameters of pulsed water jet is still not established.In this context,we aimed at developing a generalized equation for calculating rock cutting efficiency,in which all the major parameters in consideration of rock cutting process are included.Then,a calibration of the rational parameters of rock cutting by pulsed water jets was conducted.The results are likely helpful for increasing productivity and reducing energy consumption.

Gas-hydrate formation,agglomeration and inhibition in oil-based drilling fluids for deep-water drilling

One of the main challenges in deep-water drilling is gas-hydrate plugs,which make the drilling unsafe.Some oil-based drilling fluids（OBDF） that would be used for deep-water drilling in the South China Sea were tested to investigate the characteristics of gas-hydrate formation,agglomeration and inhibition by an experimental system under the temperature of 4 ？C and pressure of 20 MPa,which would be similar to the case of 2000 m water depth.The results validate the hydrate shell formation model and show that the water cut can greatly influence hydrate formation and agglomeration behaviors in the OBDF.The oleophobic effect enhanced by hydrate shell formation which weakens or destroys the interfacial films effect and the hydrophilic effect are the dominant agglomeration mechanism of hydrate particles.The formation of gas hydrates in OBDF is easier and quicker than in water-based drilling fluids in deep-water conditions of low temperature and high pressure because the former is a W/O dispersive emulsion which means much more gas-water interfaces and nucleation sites than the later.Higher ethylene glycol concentrations can inhibit the formation of gas hydrates and to some extent also act as an anti-agglomerant to inhibit hydrates agglomeration in the OBDF.

GPGPU-parallelised hybrid finite-discrete element modelling of rock chipping and fragmentation process in mechanical cutting

Mechanical cutting provides one of the most flexible and environmentally friendly excavation methods.It has attracted numerous efforts to model the rock chipping and fragmentation process,especially using the explicit finite element method(FEM) and bonded particle model(BPM),in order to improve cutting efficiency.This study investigates the application of a general-purpose graphic-processing-unit parallelised hybrid finite-discrete element method(FDEM) which enjoys the advantages of both explicit FEM and BPM,in modelling the rock chipping and fragmentation process in the rock scratch test of mechanical rock cutting.The input parameters of FDEM are determined through a calibration procedure of modelling conventional Brazilian tensile and uniaxial compressive tests of limestone,A series of scratch tests with various cutting velocities,cutter rake angles and cutting depths is then modelled using FDEM with calibrated input parameters.A few cycles of cutter/rock interactions,including their engagement and detachment process,are modelled for each case,which is conducted for the first time to the best knowledge of the authors,thanks to the general purpose graphic processing units(GPGPU) parallelisation.The failure mechanism,cutting force,chipping morphology and effect of various factors on them are discussed on the basis of the modelled results.Finally,it is concluded that GPGPU-parallelised FDEM provides a powerful tool to further study rock cutting and improve cutting efficiencies since it can explicitly capture different fracture mechanisms contributing to the rock chipping as well as chip formation and the separation process in mechanical cutting.Moreover,it is concluded that chipping is mostly owed to the mix-mode Ⅰ-Ⅱ fracture in all cases although mode Ⅱ cracks and mode Ⅰ cracks are the dominant failures in rock cutting with shallow and deep cutting depths,respectively.The chip morphology is found to be a function of cutter velocdty,cutting depth and cutter rake angle.

Characteristics of different rocks cut by helical cutting mechanism

To research the loading charactefistc of rocks with different structures cut by helical cutting mechanism （HCM）, three different structures of rock （hard-soft-hard rock, soft-hard rock and soft-hard-soft rock） were built. And each type model was further divided into three types when the experiments were carried out. To reduce the errors of cutting load caused by manually configured rock in each test, the cutting load of soft rock was taken as a benchmark, and the differences of the cutting load of the different structures of rocks and the soft rock were used to reflect the cutting load change rules of the HCM. The results indicate that, the cutting load of only the HCM top cutting hard rock is larger than that of only the HCM bottom cutting hard rock for dextral HCM, and the cutting load fluctuation is larger, too. However, when the top and the bottom of the HCM cutting hard rock simultaneously, its cutting load is the largest, but the cutting load fluctuation is the least. And the HCM cutting load increment is increased linearly with the increase of rock compressive strength. The HCM cutting load increment is increased exponentially with the increase of hard rock cutting thickness.

Influence of confining stress on fracture characteristics and cutting efficiency of TBM cutters conducted on soft and hard rock

Combined with numerical simulation, the influence of confining stress on cutting process, fracture conditions and cutting efficiencies of soft and hard rock has been conducted on the triaxial testing machine(TRW-3000) designed and manufactured in Central South University(China). Results are obtained by performing analysis on the fracture scopes of cement and granite plates,the characteristics of cutting force in cutting processes and the cutting efficiency. Firstly, the increase of latitude fracture scope and the decrease of longitude fracture scope are both more notable in the tests conducted on cement plates subjected to the increasing confining stresses; secondly, the increase tendency of peak penetration forces obtained from tests conducted on granite plates is more obvious, however, the increase tendencies of average penetration forces achieved from cement and granite plates are close to each other; thirdly, the cutting efficiency could be improved by increasing the spacing between cutters when the confining stress which acts on soft and hard rock increases in a certain degree, and the cutting efficiency of soft rock is more sensitive to the varying confining stresses.

A New System to Evaluate Comprehensive Performance of Hard-Rock Tunnel Boring Machine Cutterheads

The accurate performance evaluation of a cutterhead is essential to improving cutterhead structure design and predicting project cost. Through extensive research, this paper evaluates the performance of a tunnel boring machine(TBM) cutterhead for cutting ability and slagging ability. This paper propose cutting efficiency, stability, and continuity of slagging as the evaluation indexes of comprehensive cutterhead performance. On the basis of research of true TBM engineering applications, this paper proposes a calculation method for each index. A slagging efficiency index with a ratio of the maximum di erence between the slagging amount and average slagging is established. And a slagging stability index with a ratio of the maximum slagging fluctuation and average slagging is presented. Meanwhile, a cutting efficiency index by the weighed average value of multistage rock fragmentation of a cutter’s specific energy is established. The Robbins and China Railway Construction Corporation(CRCC) cutterheads are evaluated. The results show that under the same thrust and torque, the slagging stability of the CRCC scheme is worse, but the slagging continuity of the CRCC scheme is better. The cutting ability index shows that the CRCC cutterhead is more efficient.

Discovery of Potassium-Bearing Cuttings from the Well Yangta 4 in the Kuqa Depression and Seam Division

The world petroleum exploration suggests that,about70%of the world’s potash resources were discovered during oil and gas exploration(Zheng et al.,2007).The Kuqa depression in the Tarim basin is abundant with petroleum exploration data,and

Cutting capacity of PDC cutters in very hard rock

An experimental programm of investigating the cutting capacity of PDC flat cutters in very hard rock has been performed. Experiments include both the cutting of PDC fixed at different angles on the granite core or bar and linear cutting with different static thrust on the block of granite. The effects of the rough degree of rock surface, cutting angles, and static thrust on the cutting capacity of PDC in very hard rock were investigated and analyzed. The results show that the single mode of rotary drilling using PDC cutters is not applied for very hard rocks.

Experimental investigation on the cuttings formation process and its relationship with cutting force in single PDC cutter tests

The single polycrystalline diamond compact(PDC)cutter test is widely used to investigate the mecha-nism of rock-breaking.The generated cuttings and cutting force are important indexes reflecting the rock failure process.However,they were treated as two separate parameters in previous publications.In this study,through a series of rock block cutting tests,the relationship between them was investigated to obtain an in-depth understanding of the formation of cuttings.In addition,to validate the standpoints obtained in the aforementioned experiments,rock sheet cutting tests were conducted and the rock failure process was monitored by a high-speed camera frame by frame.The cutting force was recorded with the same sampling rate as the camera.By this design,every sampled point of cutting force can match a picture captured by the camera,which reflects the interaction between the rock and the cutter.The results indicate that the increase in cutting depth results in a transition of rock failure modes.At shallow cutting depth,ductile failure dominates and all the cuttings are produced by the compression of the cutter.The corresponding cutting force fluctuates slightly.However,beyond the critical depth,brittle failure occurs and chunk-like cuttings appear,which leads to a sharp decrease in cutting force.After that,the generation of new surface results in a significant decrease in actual cutting depth,a parameter proposed to reflect the interaction between the rock and the cutter.Consequently,ductile failure dominates again and a slight fluctuation of cutting force can be detected.As the cutter moves to the rock,the actual cutting depth gradually increases,which results in the subsequent generation of chunk-like cuttings.It is accompanied by an obvious cutting force drop.That is,ductile failure and brittle failure,one following another,present at large cutting depth.The transition of rock failure mode can be correlated with the variation of cutting force.Based on the results of this paper,the real-time monitoring of torque may be helpful to determine the efficiency of PDc bits in the downhole.

Rock Cutting Analysis Employing Finite and Discrete Element Methods

The petroleum industry has shown great interest in the study of drilling optimization on pre-salt formations given the low rates of penetration observed so far. Rate of penetration is the key to economically drill the pre-salt carbonate rock. This work presents the results of numerical modeling through finite element method and discrete element method for single cutter drilling in carbonate samples. The work is relevant to understand the mechanics of drill bit-rock interaction while drilling deep wells and the results were validated with experimental data raised under simulated downhole conditions. The numerical models were carried out under different geometrical configurations, varying the cutter chamfer size and back-rake angles. The forces generated on the cutter are translated into mechanical specific energy as this parameter is often used to measure drilling efficiency. Results indicate that the chamfer size does not change significantly the mechanical specific energy values, characteristic. Results also show there is a significant increase although the cutter aggressiveness is influenced by this geometrical in drilling resistance for larger values of back-rake angle.

刃宽对硬岩掘进影响的仿真及试验研究

滚刀在硬岩掘进中极易发生崩刃、偏磨等异常失效,研究硬岩掘进条件下刃型参数对滚刀破岩载荷和破岩效率的影响十分重要.本文采用滚刀破岩试验和仿真分析相结合的方法,从载荷曲线、破岩体积、破岩比能等方面分析了刃宽对滚刀破岩的影响.基于双线性本构模型及Benzeggagh–Kenane损伤断裂准则建立了岩石材料的内聚力本构模型,通过单轴抗压试验及巴西劈裂试验对内聚力本构模型的微观参数进行了校准,并进一步建立了滚刀破岩的内聚力仿真模型.结果表明:内聚力本构模型可以准确的模拟破岩过程中岩石裂纹的萌生和扩展过程.依据裂纹的萌生和扩展情况,滚刀破岩过程主要分为三个阶段:弹性阶段、裂纹萌生–扩展阶段及岩石破坏卸载阶段.滚刀破岩载荷和破岩体积随着贯入度、刀间距和刃宽的增加而增加;破岩比能随刃宽的增加呈先减小后增大的趋势.对于所选取的硬岩,采用13 mm刃宽滚刀破岩时比能最小,破岩效率最高;7 mm刃宽滚刀破岩时无法形成贯通岩片,相邻滚刀之间仍存在岩脊,破岩效率较低.

预切缝辅助TBM滚刀破岩贯入荷载演化规律

基于全断面隧道掘进机(Tunnel Boring Machine,TBM)滚刀贯入室内模型试验,研究了3种不同破岩模式(完整岩样破岩、同轨迹破岩和异轨迹破岩)在不同围压条件下高强度花岗岩样贯入荷载演化特征,重点揭示贯入荷载-贯入度特征曲线、峰值荷载、最大跌落幅值变化规律,获取不同破岩模式在不同围压条件下TBM滚刀受力特性。结果表明:1)高围压组贯入荷载-贯入度特征曲线较低围压组先跌落,跌落幅度较小,但其对应的贯入荷载并非峰值荷载,而低围压组初次跌落荷载为峰值荷载,且跌落幅值较大;2)在中高围压10~15 MPa时,峰值荷载及贯入荷载最大跌落幅值均最小,表明此围压范围较利于TBM的掘进;3)低围压条件下选用异轨迹破岩模式较同轨迹破岩模式能更有效地降低TBM滚刀贯入荷载,但同轨迹破岩模式的岩样发生楔裂破坏,其最大跌落幅值最小,更能减少刀具所受冲击荷载,减少刀具磨损。

纵轴岩巷掘进机截割部故障分析

主要介绍了纵轴岩巷掘进机截割部的组成和工作原理。通过对截割部结构分析,结合现场经验,总结了一些常出现的故障现象,对其原因进行分析并提出应对措施,可以帮助维修人员快速判断和解决问题,也为截割部的设计提供依据。

基于FEM-SPG耦合的盾构滚刀破岩仿真研究

隧道施工过程中岩石在盾构滚刀破岩力的作用下会发生破碎,传统的有限元方法(FEM)无法探究这一现象。为解决使用FEM面临网格畸变及无法同时分析岩石破碎的问题,引入光滑粒子伽辽金(SPG)分析方法,通过FEM和SPG耦合的方式建立了滚刀回转切削岩石模型。结果表明:FEM-SPG方法能够有效地展示岩石的密实核破碎过程及岩渣飞溅的现象。通过与CSM模型进行对比验证,发现仿真得到的滚刀垂直力与CSM模型相比误差为1.8%,验证了模型的可靠性。该方法与模型能够为滚刀精准破岩研究及分析岩石破碎机理提供新思路。

动压巷道围岩变形机理及其控制技术研究

针对寺河煤矿二号井动压巷道在工作面回采过程中存在的围岩变形严重及工作面支架阻力过大等问题,采用现场监测与数值模拟相结合的手段,对动压巷道围岩变形机理及其控制技术进行了系统研究。结果表明,巷道在经受掘进支护及工作面的开采动压影响后,围岩应力水平升高,且两侧应力不平衡,帮部不对称变形严重,巷道围岩变形主要分为单侧采用影响与两侧采动影响2个阶段,巷道变形主要是因为采区大巷两侧工作面采动产生的应力扰动作用,导致巷道承载性能持续恶化,围岩发生反复变形破坏。据此,研究提出采用预裂切顶卸压技术对动压巷道变形实施有效控制,确定合理的切顶卸压高度与角度分别为16.5 m与60°。通过现场实践,对动压巷道实施切顶卸压后,围岩顶底板及两帮移近量较卸压前得到了有效控制,工作面支架阻力显著降低,保证了工作面动压巷道围岩的稳定。

Drag pick cutting tests: A comparison between experimental and theoretical results

This paper aims at reporting the results of a number of drag pick cutting tests on selected igneous rock samples to compare the experimentally determined maximum cutting force （FC） values with theoreti- cally estimated ones. First, a review on theoretical rock cutting models proposed for both chisel and conical picks was presented in detail. Experimental study consists of both chisel and conical pick cutting tests in unrelieved （single-pick） cutting mode with varying cutting depths. FC＇ values were determined from experimental results, and theoretical models were utilized to compute FC for all cutting conditions. Computed and experimentally determined F（ data were then compared for a referenced cutting depth. It is shown that the theoretical models might overestimate or underestimate FC＇ and cannot give reliable results. Finally, explanations for these mismatches were presented.

Clearance angle and evolution of depth of cut in actuated disc cutting

This paper investigates the effect of cutter clearance angle on variation of depth of cut and cutting process with an actuated disc cutting(ADC).ADC is a cyclic cutting method with two main characteristics:(i)a disk-shape cutter is used to attack the rock in an undercutting mechanism;and(ii)the cutter is dynamically actuated as it is moved across the rock.Hence,the cutting process of such system is periodic,each recurrence known as actuation cycle.The first ADC model,developed in 2016,represented an idealization of the technology with a flat disc cutter,where no clearance angle was considered.The evolution of the contact between the disc and the rock was,therefore,computed only on horizontal x-y plane,ignoring the effect of normal component of the force acting on cartridge.This article reports on a study that incorporates the cutter inclination angle in derivation of cutter/rock interface laws.It extends the proposed kinematic and geometry based model to take into account the variable depth of cut in estimating the forces associated with cutting in one actuation cycle.Experiments were conducted using Wobble to test the predictions of the improved model at various operating conditions.The model predictions are matched with the experimental results and effects of various factors are analysed.

A novel V-cut method for explosive-free breakage of biaxially loaded rock using soundless chemical demolition agents

Interest in soundless chemical demolition agents(SCDAs),also known as expansive cements,as potentially viable alternatives to explosives for rock fragmentation,has been growing in recent years.Consequently,there is an increasing amount of literature on the use of SCDA for the breakage of rock blocks and boulders.Limited research has been conducted so far on the breakage of excavation fronts,such as tunnel or drift faces,using SCDA.This is due to the perception that the planar compressive in-situ stresses in the face would inhibit the creation and propagation of fracturing due to expansive pressure.This study proposes a novel V-cut method for demolishing rock panels under biaxial stress using SCDA.This method was examined through large-scale tests and numerical modelling.The rock panels were subjected to high biaxial confinements of 26 MPa and 40 MPa.Such a level of confinement corresponds to an in-situ stress state 1000 m below the surface in the Canadian shield.The V-cut drillhole pattern employs two sets of three SCDA holes angled at 45
from the face of a Stanstead granite panel.The drillhole arrangement aims to create a V-shaped wedge in the plane of major principal stress.When angled drillholes are subjected to expansive pressure,they tend to cast out of the panel face,causing fragmentation.Two panels of 1 m1 m0.25 m were successfully demolished using the proposed method.The three-dimensional fast Lagrangian analysis code FLAC3D modelling was used to reconstruct the panel failure mechanism owing to the V-cut.This study demonstrates the feasibility of fragmenting an excavation front,such as a rock excavation face,with SCDA using a V-cut drill hole pattern while subjected to high biaxial confinement.

Pyrolytic gas analysis and evaluation from thermal plasma pyrolysis of simulated oil-based drill cuttings

Oil-based drill cuttings(OBDCs)are hazardous wastes generated during shale gas exploration,and the rapid,efficient and safe disposal methods for OBDCs have attracted the attention of many researchers.Plasma pyrolysis technology is widely used in solid waste treatment due to its extremely high temperature and reaction activity.A laboratory-scale thermal plasma pyrolysis system was built to investigate the plasma pyrolysis mechanism of simulated OBDCs.The thermal decomposition characteristics of OBDCs were studied by thermogravimetric-derivative thermo gravimetric-differential scanning calorimetry(TG-DTG-DSC)analysis in the range of 50–1300℃.The thermal decomposition process of OBDCs was divided into the following four stages:evaporation of water and light oil,evaporation and decomposition of heavy oil,carbonate decomposition,and phase change reaction from solid to liquid.The effects of the oil ratio,water content,and water/oil(W/O)ratio of OBDCs on the composition and gas selectivity of pyrolytic gas were investigated.The results show that thermal plasma can crack the mineral oil in the OBDCs into clean gases such as H_(2),CO and C_(2)H_(2),while water can promote the decomposition of the heavy oil molecules and enhance the H_(2)production.The energy consumption model calculation for the pyrolysis and melting of OBDCs shows that the highest energy utilization and the lowest molar energy consumption of H_(2)were achieved at a W/O ratio of 1:4.Based on the thermal plasma pyrolysis system used in this study,the commercial application prospects and economic benefits of the plasma pyrolysis of OBDCs were discussed.